Interesting...it's on mine, too. I couldn't find any explanation on the AT&T website.
Edit: I found this information on another forum that explains some features on the 3G plan:
The UMTS auto attach is just giving you access to the 3g internet. UMTS is 3g.
Upgrade tracking code goes on the 3g and 2g iphone. It just shows at&t that you upgraded your phone. It's also (I think) what is letting the old 2g customers get their new iphones at the discounted price.
Iphone 3g trkg is just telling at&t that you got a 3g iphone.